Look at the feed you're sending to froogle / google base. Make sure the image paths are correct. Make sure your images are larger than 100 / 100 and they are in jpeg or gif format. Make sure that your images are stored on the file system. If your image urls end in "product_image.php?productid=12345" then your images may get rejected.

If you have checked all of the above and everything is correct, then ask google why your images are not showing up.